1. Field of the Invention
The present invention relates to a process for manufacturing steel sheets or various types of steel members used as substrates for bonding (hereinafter, will be referred to as steel) which are treated with zinc-silica composite plating.
2. Prior Art
The process for galvanization has been used for ornamental plating of steel by aiming at beautification of appearance with emphasis focused on how to form the smooth surface.
In spite of the conventional background in the use of galvanization process mentioned above, recently, for example, for automobiles, with sophistication of products as well as expansion in geographical areas they are used in, the durability in terms of rust prevention became the requirement of them, and the galvanization has began to be applied also to the substrates for coating or rubber bonding.
However, in the case where the coating is applied onto the zinc plated steel or where the organic polymer materials (organopolymeric materials), such as rubber, are adhered onto the zinc plated steel, there has been the limit in improvement of adhesion no matter what arrangement is made for the composition of paint and the polymeric material, or even when the surface preparation agent, such as primer, adhesive, is provided between the steel and the paint.
Accordingly, various methods have been studied for treating the surface of the steel which has been galvanized (zinc plated) in order to prepare the steel surface for bonding, and such methods have been put in practical use. Those methods include (1) chemical treatments, such as chemical conversion process for forming the phosphate film through phosphate coating, or chemical conversion process for forming the chromate film through chromic acid coating; and (2) physical treatments to obtain the wedge (anchoring) effect through giving the irregularity to the surface of steel plate by means of sand blasting, grit blasting, etc. In other words, unlike the conventional purpose of galvanization, that is to provide the zinc plate surface with smoothness, the purpose of the method mentioned above is to make the surface as rough as possible.
The method using the phosphate mentioned in (1) is most widely used as the treatment process for the steel surface after the galvanization. However, it has the problems in the treatment of the waste water and the disposal of large amounts of sludge. Also, the treatment with chromic acid does not always give the satisfactory effect of adhesion needed as substrate coating. Besides, it has the problems of toxicity of chromium and the waste water treatment.
The physical process using the sand blasting, etc. that is mentioned in (2) also is not free of difficulties. That is, it is hard to provide the plate with irregularity that is sufficiently fine and complex to fully show the anchoring effect. Furthermore, such methods are not suitable for bent shape and small members. In addition, the irregularity cannot be provided for all the corners of the member.
It is mentioned in U.S. Pat. No. 4,089,755 and U.S. Pat. No. 4,444,630 that the alkyl-substituted (alkylated) ammonium salt is added as migration agent in the zinc plating bath in order to polish the zinc plate. Also, U.S. Pat. Nos. 3,844,910 and 4,222,828 disclose the process for forming the coprecipitation deposit with metal through suspending inorganic grains in metal plating bath as a method for providing the surface of the plate with roughness, sliding capacity, wear resistance and corrosion stability.
However, the U.S. Pat. Nos. 4,089,755 and the 4,444,630 are different from the present invention in purpose. The patents disclose alkyl-substituted ammonium salt, and the purposes are to effect the polishing of the zinc plate surface. However, use of the coprecipitation system with the silica fine grains is not disclosed.
The object of the present invention is rather contrary to that aimed at by the foregoing prior art. That is, what is intended by the present invention is to eliminate the smoothness of the plate surface and thus to bring about the anchoring effect on the paint and adhesive even without giving the after-treatment, through the electrolyzation carried out by adding the cationic surface active agent into the zinc-silica composite plating system.
In the process for manufacturing metal coating products provided by the U.S. Pat. No. 3,844,910,for the Ni plating, gamma-amino-propyltriethoxysilane is added for the coprecipitation with SiC presenting as nonmetallic particles. In this manufacturing process, a similar substance to the silane coupling agent used in the present invention is used as the dispersant for SiC.
Similar to U.S. Pat. Nos. 3,844,910, 4,222,828 uses the Ni-plate as primary body. In this invention, in order to improve the coprecipitation state in the Ni-SiC composite plating, the electrolyzation is performed by using the cationic fluorocarbon activator and KNO.sub.3 at the Zeta potential of at least +40 mV. In U.S. Pat. No. 4,222,828 as the object of the metallic plating, Zn is disclosed. Also, as the nonmetallic grains for coprecipitation, SiO.sub.2 is described. However, they are merely listed with no detailed description given on the conditions of the electrolyzation. Further the invention does not intend to obtain the substrate steel sheet that is satisfactory in adhesion to the adhesive agent and the primer of paint, as intended by the present invention.